Try taking the cabinet cover off the amp, so more air can circulate. I have a McIntosh MC402 and MD205, both in a audio cabinet. I have only had my 205 go into thermal shutdown once for a movie. I cut 4 2.5" holes inthe bottom of cabinet(audio not amp) and that let more air convect thru to dissapate the heat and never have had an issue again. As far as the 402 it has never had an issue with heat.
